1. Field of the Invention
The present invention relates to a perfume or perfume intermediate used in fragrant cosmetics, and more particularly, to the trans form of (1S,6R)-2,2,6-trimethylcyclohexyl methyl ketone and/or (1R,6S)-2,2,6-trimethylcyclohexyl methyl ketone, a process for producing the same and a perfume composition containing the same.
2. Description of the Related Art
Although the reports given below have been made with respect to 2,2,6-trimethylcyclohexyl methyl ketone (1), none of these reports relate to its fragrance. As an example of synthesis of the racemic form, 2,2,6-trimethylcyclohexyl methyl ketone (1), James D. White et al. (J. Org. Chem. (1978), 43(23), 4555-4556) synthesized 2,2,6-trimethylcyclohexyl methyl ketone (1) by hydrogenating 2,6,6-trimethyl-1-cyclohexenyl methyl ketone (3) with a ytterbium catalyst in liquid ammonia as indicated by the formula below at yield of 81% (the ratio between the cis and trans forms is unknown). 
In addition, as indicated by the formula below, R. A. Barnes et al. (Int. Cong. Essen. Oils, 7th (1979), Meeting Date 1977, Volume 7, 253-256, Publisher, Japan Flavor Fragrance Manufacturers"" Asso., Tokyo, Japan) describes a method characterized by obtaining homocitronellol (5) by reacting citronellal (4) with methyl magnesium chloride followed by cyclization with acid, while yield and the ratio between the cis and trans forms are unknown. 
As indicated by the formula below, M. Chatzopoulos et al. (Revue Roumaine de Chimie, 26, 2, 275-282 (1981)) synthesized 2,2,6-trimethylcyclohexyl methyl ketone (1) at a yield of 30% using 4,8-dimethylnonan-2-one (6) and a radical initiator (D.T.B.P.). The ratio between the cis and trans forms is unknown in this case as well. 
In addition, as indicated by the following formula Douwe R. De Haan et al. (Japanese Patent Publication No. 57-36252, DE 2353578) synthesized cis-2,2,6-trimethylcyclohexyl methyl ketone (racemic cis-(1)) by hydrogenation of 2,6,6-trimethyl-3-cyclohexenyl methyl ketone (9) obtained in a Diels-Alder reaction between 1,3-pentadiene (7) and mesityl oxide (8), and synthesized trans-2,2,6-trimethylcyclohexyl methyl ketone (racemic trans-(1)) by treating the racemic cis-(1) with polyphosphoric acid. 
With respect to optically active substances, Richard Buchecker et al. (Helv. Chim. Acta (1973), 56(7), 2548-2563) reported the cis form indicated by the following formula, namely the (1R,6R) form (formula (1c)) and/or the (1S,6S) form (formula (1d)). 
However, they derived and synthesized these compounds from the viewpoint of research on the absolute structure of xcex1-cyclogeranic acid, xcex1-cyclogeranial, xcex1-ionone, xcex3-ionone, etc., and there is no description of their fragrance. In addition, there is no mention of the trans forms that are the compounds of the present invention, namely the (1S,6R) form represented by the formula (1a) and/or the (1R,6S) form represented by the formula (1b), and these were not known compounds.
On the other hand, the fruity floral perfume, 1-(2,2,6-trimethylcyclohexyl)-2-buten-1-one (10) is a known example of a perfume that is derived from 2,2,6-trimethylcyclohexyl methyl ketone (1). With respect to the racemic forms of this compound, according to the previously mentioned Douwe R. De Haan et al. (Japanese Patent Publication No. 57-36252, DE 2353578), the cis and trans forms of 1-(2,2,6-trimethylcyclohexyl)-2-buten-1-one (Racemic cis-(10)) and (Racemic trans-(10)) are produced by the method indicated by the following formulas: 
(wherein wave lines indicate the cis or trans form).
In addition, with respect to the optically active 1-(2,2,6-trimethylcyclohexyl)-2-buten-1-one (the (1S,6R) form is referred to as (10a), while the (1R,6S) form is referred to as (10b)), the inventors of the present invention synthesized this optically active compound using the method indicated below (in accordance with Japanese Patent No. 2748184) using optically active dihydrocyclocitral ((1S,6R) form (formula (11a) and/or (1R,6S) form (formula (11b)) as the starting material, and found there to be a considerable difference in fragrance between the enantiomers, and that both exhibit superior fragrance characteristics that are different from the racemic forms. 
In recent years, with respect to perfume materials as well, there has been a need to develop novel perfume materials having unique and superior fragrance characteristics due to the increasing diversification of fragrant cosmetic products. With respect to characteristic perfume materials such as eucalyptus, mint-like and white floral perfume materials in particular, there has been a growing demand to develop novel perfumes from perfumers. On the other hand, optically active trans-(1R,6S) and/or (1S,6R)-2,2,6-trimethylcyclohexyl-2-buten-1-one (10), a superior fruity floral perfume, has fragrance characteristics that are superior to its racemic forms, and is desired to be used in high concentrations in terms of formulation. However, as a result of its high price placing limitations on its use, there has been a desire to develop a less expensive production method.
A first object of the present invention is to provide a unique and superior eucalyptus, mint-like or white floral novel perfume material for which there is a high demand for development from perfumers, along with a method for economically producing such a perfume material.
A second object of the present invention is to enable more economical production of optically active trans-(1S,6R)- and/or (1R,6S)-2,2,6-trimethylcyclohexyl-2-buten-1-one (10).
As a result of conducting earnest studies in consideration of the above circumstances, the inventors of the present invention found that the following novel trans forms of (1R,6S)- and/or (1S,6R)-2,2,6-trimethylcyclohexyl methyl ketone have unique and superior eucalyptus, mint-like and white floral-like fragrances different from their racemic forms, and that they are extremely useful as a novel perfume material. In addition, with respect to a production method, the inventors of the present invention also developed an inexpensive, novel production method, and accomplished the present invention. It should be noted that, as a result of allowing these novel optically active trans-2,2,6-methylcyclohexyl methyl ketones ((1S,6R) form (1a) and/or (1R,6S) form (1b)) to be produced with a novel inexpensive method, by using these as starting materials, it has become possible to provide optically active trans-1-(2,2,6-trimethylcyclohexyl)-2-buten-1-one ((1S,6R) form (10a) and/or (1R,6S) form (10b)) having superior fragrance characteristics as compared with their racemic forms less expensively than by the methods of the prior art.
Namely, the present invention provides trans-2,2,6-trimethylcyclohexyl methyl ketone, which is (1S,6R)-2,2,6-trimethylcyclohexyl methyl ketone represented by the formula (1a): 
and/or (1R,6S)-2,2,6-trimethylcyclohexyl methyl ketone represented by the formula (1b): 
as well as a process for producing trans-2,2,6-trimethylcyclohexyl methyl ketone represented by the above formula (1a) and/or the formula (1b), the process comprising cyclizing a novel optically active enol acetate represented by the formula (2a): 
and/or the formula (2b): 
(wherein Ac represents an acetyl group; double lines composed of solid lines and broken lines represent a double bond or a single bond; Z represents a hydroxyl group or methoxy group in the case the double lines represent a single bond; and Z is not present in the case the double lines represent a double bond) in the presence of an acid catalyst.
Other aspects and advantages of the invention will become apparent from the following description illustrating by way of example the principles of the invention.